Fix subtle bug in reading of zero-length strings, which caused crashes on loading.
Fix the crash in rdwr_string differently.
Revert "Fix the crash in rdwr_string differently."

This reverts commit 40d734881d3f1416ea60f5af05d0ac4074438fbb.
Revert "Fix subtle bug in reading of zero-length strings, which caused crashes on loading."

This reverts commit 8cc12ef7eb588d9f18bfdd5e687e60068463b1d9.